Microscope-on-a-chip debuts

PORTLAND, Ore.  Today's bulky, expensive microscopes could be come smaller and cheaper after researchers found a way to combine pinhole optics, microfluidics and a charge-coupled device (CCD) to assemble a working microscope on a single chip.

Small enough to fit in a mobile phone or similar handheld device, the optofluidic microscope developed by California Institute of Technology engineers requires only sunlight for illumination, and could be mass-produced for $10. Caltech hopes to work with a manufacturing partner to produce handheld versions for remote monitoring. Applications could include malaria screening or identifying pathogens on the battlefield.

The device is also small enough to be implanted in the body, constantly monitoring blood circulation to help slow the spread of cancer and other diseases.

The device is based on a CCD sensor with a coated metal film on top. A line of submicron holes, spaced five microns apart, was then etched into the metal film. The holes, corresponding to each pixel on a sensor array, then have a microfluidic channel etched in a transparent material on a diagonal above the line of holes. A sample is then flowed through the channel, either by gravity or by a small voltage potential, and the entire assembly is illuminated with sunlight.

As samples pass over the holes, any objects in the fluid progressively block light in the series of holes, producing a series of partial images which are recorded by the CCD. The series of light-and-shadow images, similar to the images form a pinhole camera, overlap. However, since the holes are diagonal across the microfluidic channel, each one captures a different part of the object's image, which is reassembled into a complete image by algorithms performed on the chip.

The finished image is then displayed for identification.

The Caltech researchers claimed thousands of optofluidic microscopes could be integrated above a single CCD, each using different lines of pixels that would allow many organisms to be simultaneously imaged and analyzed.

Funding for the microscope chip researcher was provided by the Defense Advanced Research Projects Agency, Caltech's Center for Optofluidic Integration, the Wallace Coulter Foundation, the National Science Foundation and the National Institutes of Health.